Anchoring

[Sea Devil]

May I ask a couple of questions from professionals please?

What is the process of anchoring a big ship?

Is it all controlled electronically from the bridge?

How much chain to depth do you lay out?

Do you rely on the weight of the anchor and chain or do you go astern to dig the anchor in?

In places like Gibraltar, Algerciras Bay, does the 'pilot' give you a lat long position for the centre of your swinging circle or do you do it by 'eye'?

Many thanks

Michael

 

[richardhilton590]

I've got the same questions for a thesis I am working on. I hope to hear from our professionals here! There are answers on google but it very much generalized.

 

[homa]

Very few ships can drop an anchor from the bridge
My present ship can but that's it. We can only drop the anchor, cannot heave it back in. Only ever dropped from bridge in case of emergency.
Normal procedure for anchoring is exactly the same as in any boat. Man sent forward and removes compressor from anchor cable either puts windlass in gear to partly walk out cable, alternatively stands by the brake and opens brake on command from the bridge. When brake is opened there is a lot of heavy metal moving quickly, man needs to have eye and ear protection and stand clear as much as possible.
Apart from checking the depth of water, probably the most important thing is checking the available room to swing the ship.
Anchor is dug in but we use the momentum of the ship drifting astern rather than use engines, equipment is heavy, ships have a lot of mass and people are vulnerable. Anchor's primary function is to help hold the chain in position on the sea bed. The weight and friction imposed by the chain is what holds the ship in place.
We don't just use an anchor for anchoring. We also use it for docking sometimes with an onshore wind will dredge the anchor, I.e. Lower onto bottom and use it as a dead weight to slow drift towards berth.
Have also used an anchor on more than one occasion to stop bow hitting quay when thruster failed. Used inside anchor, it drops onto river bed, runs under bow and digs in very quickly, disadvantage is it takes a lot of paint off and can damage the hull. I drive a ferry and these can be a bugger to anchor in all but no wind. On the few times we have ever had to anchor in an anchorage we never laid to the wind, always beam on to the wind and sea so rolled and dragged. I will only anchor if it is flat calm and no swell, prefer to drift or steam slowly otherwise. In practice, we are in service 99.9pc of the time so it is not really an issue.

 

[ronsurf]

There is a YouTube clips of a US Navy ship running out of anchor chain. The expressions (and language) of the crew as the end of the chain disappears overboard is classic.

 

[Richard10002]

All the way to the bitter end!

 

[Sea Devil]

Thanks for telling me about big ship anchoring.... As they pull into Gib/Algerciras Bay they just seem to pull up and drop the hook... No small boat 'digging' it in etc and now I understand. Huge anchor and enormous chain is the answer. I found when I was long distance cruising that the answer was to upgrade the chain one size and the anchor size...

Most grateful for the info - I am going to look for the UTube of the US warship when I am next in port

best wishes

Michael

 

[noelex]

Huge anchor and enormous chain is the answer. I found when I was long distance cruising that the answer was to upgrade the chain one size and the anchor size...

Large ship anchoring tactics don't translate well to our sized yachts. The scale difference is just too large. In particular large ships rely mostly on the holding power of the chain. This does not work for our sized vessels, because in strong wind the chain is not on the bottom.


There is not a great deal of opportunity to observe large ships in the same anchorage, but I have seen them drag in reasonably benign conditions so I suspect they do no better than we do.

 

[Sea Devil]

Really interesting . I did suspect that huge merchant ships did not really attempt to dig the pick in....but if they started to drag no doubt it would....

I think yachts tend to be sold with the minimum size chain and anchor advisable. It's really only in the Caribbean or South Pacific where you are anchoring every day or at anchor every day does that become an issue...

Sadly all the places here in the med i used to anchor in are marinas or forbidden - still that's progress. On my way towards Palermo - currently - https://www.vesselfinder.com/ - Paw Paw of London.
Do not want to start another silly anchoring series of posts - I just become more and more interested in the way big ship professionals do things.
Michael

 

[mm42]

If you see the size of the anchor on a big ship up close it will make sense, on a powerboat course we sailed close up to a cruise ship for a look at it close up, one of his anchors was bigger than the 6.5m RIB I was driving!

 

[Sea Devil]

Yes they are huge but compared to the size or 'boat' they are joining to the sea bed probably a similar size proportionally as ours... I think...

 

[Bilgediver]

On some big ships the anchoring process s totally manual however there are various add ons available to make life easier such as chain footage counters etc. Chain used to be supplied in 90 foot lengths joined by kenter link shackles and so was measured in shackles depending how many paid out. Modern chain making equipment can make chain by a continuous process so no shackles

Anchoring in a crowded anchorage is usually planned so that the ship comes up to the allocated slot already heading the same way as other anchored ships and all way will be taken off by either engines or wind and tide. Some help may be given to moving the ship astern however once the ship is moving it will have enough inertia to do the job. Up on the for deck the first officer will have walked the anchor out till it is clear of the Hawse pipe. He will then secure the brake and declutch the drive. On receipt of the command let go he will release the brake on the windlass and allow the anchor to fall to the sea bed at which point he will start to control the rate of pay out of chain so it is laid on the sea bed correctly and not in a pile! As the chain goes out he will advise the bridge officer how much chain is in the water. The bridge officer will tell him when to secure the windlass. The ship moving astern will dig the anchor in! A watch will b kept to ensure the anchore holds.

 

[Sea Devil]

Thank you for that explanation - May I ask you a couple more questions please?

In Gibraltar/Algerciras bay I assume it is the pilot who 'allocates' the anchoring spot - either Gib or Spanish?

How much chain to depth is normally let out assuming reasonable conditions?

I assume with so many crew on a merchant ship anchor watch is 24/7

Michael

 

[Bilgediver]

Usually anchoring is done to the instructions of harbour control unless outside harbour limits when a pilot might not be required so at masters discretion. The master would decide on the scope of anchor chain taking into account the type of holing ground,effect of wind and current and expected swell. Anything between X3. to X6 water depth.

 

[dancrane]

Fast-forward to four minutes forty-five seconds in, for that desperate uncontrolled few seconds, reminiscent of We Didn't Mean To Go To Sea...

 

[arjohn]

A very interesting video, there must have been some red faces around after that incident,hard to see how that could happen, the clue might be in the way the two men were were wrestling with what was presumably the brake--!

 

[Biggles Wader]

Ive seen that happen twice,although neither time did we lose the entire cable,caused by overheating of the windlass brake and then total failure of same.Each time we stopped it by throwing the stopper bar over the cable as it "paused".It can be tricky to pull it all back in again on a 12000 ton ship in a narrow canal.

 

[dombuckley]

Usually anchoring is done to the instructions of harbour control unless outside harbour limits when a pilot might not be required so at masters discretion. The master would decide on the scope of anchor chain taking into account the type of holing ground,effect of wind and current and expected swell. Anything between X3. to X6 water depth.

A good rule of thumb is No of shackles (90' lengths) = 1.5 x sqrt water depth (metres). So about 5 shackles (450') in 10m depth, 6 shackles (540') in 15m, 7 shackles (630') in 20m, 8 shackles (720') in 30m.

Big ships rely on the weight of cable on the bottom, so the simple linear 3x water depth is rarely sufficient.

 

[Richard10002]

A good rule of thumb is No of shackles (90' lengths) = 1.5 x sqrt water depth (metres). So about 5 shackles (450') in 10m depth, 6 shackles (540') in 15m, 7 shackles (630') in 20m, 8 shackles (720') in 30m.

Big ships rely on the weight of cable on the bottom, so the simple linear 3x water depth is rarely sufficient.

I don't actually know the answer but, are we sure they rely on weight of chain?

When I reached the dizzy heights of Third Officer in a previous life, I recall the vessel being motored astern to the point where the anchor chain became taught and then slackened, which suggested/confirmed that the anchor was dug in - not dissimilar to what we do on our "little boats".

There was a special marine word for what the chain did when tightening then slackening, but I can't remember it.

 

[S1975]

Richard,

The word/expression is "brought up" to the anchor or cable. I am sure it would have come back to you.

To those whom it may be of interest.

In regards to digging the anchor in by moving astern slowly, some ships do and I always feel more comfortable doing it that way, just as on my little motor cruiser. As another poster indicated the forces involved can be large so it is done gently usually at about 1 knot, tickling astern on one shaft.

In some ports an anchor position is indicated by port control, on the chart or by the pilot, whose good advice we will take. If not we will anchor clear of channels, dangers and other ships/yachts taking careful note of the anchor swinging circle extremity at the stern.

Hope that helps.

Regards

S1975 (Still a serving shipmaster)